Bonanza Creek Experimental Forest: Active layer depths at core floodplain sites

Annual thaw depths are measured at the time of maximum thaw at any of the 35 BCEF-LTER sites that have permafrost or intermittent seasonal frost. 1. Wildfire in the black spruce permafrost sites will cause an increase in the active layer thickness and subsidence of the surface layers that may last for up to 25 years. The active layer thickness should return to the pre-fire depths between 25 and 30 years after the fire. 2. Climate warming in interior Alaska may result in an increase in the active layer thickness in black spruce permafrost sites. 3. Fire and climate warming together may result in the elimination of permafrost from some black spruce permafrost sites in interior Alaska. 4. Forest succession on the floodplain of the Tanana River results in a gradual decrease in soil temperature as the organic layer increases with time. The development of a thick feathermoss layer in later stages of succession is especially important in the development of permafrost. Permanent or intermittent permafrost should develop in the older white spruce stages. Black spruce stands on the older terraces should be underlain by permafrost with a shallow active layer. 5. Climate warming will delay the formation of permafrost until the latest stages of forest succession and may eliminate it completely from floodplain stands.